{# 定义宏 #}
 {% macro form (action,value='登陆',methods='post') %}
     <form action="{{action}}" method="{{methods}}">
      <p>用户：</p>
      <input type="text" name="username" placeholder="用户名">
      <input type="password" name="password" placeholder="密码">
      <input type="submit" value="{{value}}">
     </form>
 {% endmacro %}